Check out the ‘GrowlerFloebergOrFloebit’ class - is it correct? If so, document, else fix

[rduerr]

from ESIP report:

We detected a class ‘GrowlerFloebergOrFloebit’ which is actually all things which are Growlers, Floebergs, or Floebits. It is a subclass of Iceberg, while Growler is not specified as a subclass of Iceberg. We posit that this may be a modeling error.

[rduerr]

This class is only in sigrid3